An analog-to-digital converter (ADC) is used to convert an analog output from an analog signal source (e.g., an analog sensor) to a digital code. For instance, an ADC can be used for temperature measurement in a semiconductor device such as a Flash memory. In a semiconductor device, temperature information from a temperature sensor and an ADC can be delivered to a microcontroller. Voltage values for various semiconductor operations (e.g., read, write, program, and erase) are adjusted accordingly by the microcontroller based on the temperature information to improve the semiconductor's operational characteristics such as voltage distribution margins.
When an analog sensor and an ADC block are used, it usually takes time ranging from a few hundreds of nano-seconds to a few micro-seconds for a startup and analog-to-digital (AD) conversion.
Concerning a “startup time,” every analog circuit needs some time to reach a stationary DC state after an enable signal is applied. In a startup operation, DC bias currents and DC bias voltages for the components of an analog circuit need to start from 0 (or from a predetermined value) and reach their respective stationary values. This time can be thus defined as a “startup time,” and the phase for which the analog circuit reaches its stationary state is usually indicated as a “startup phase,” An analog sensor and an ADC operate in the same manner for their startup.
On the other hand, a “conversion time” is usually regarded as the time needed by an ADC to convert an analog signal from an analog sensor to a digital code after both circuits have reached their stationary state, and the corresponding phase can be indicated as a “conversion phase”.
In some cases, these two phases (i.e., the startup phase and the conversion phase) are not separable, and they could take place simultaneously. In these cases, it is not possible to distinguish between the startup time and the conversion time.
Usually, an analog sensor and an ADC need a certain period of time, which may range from some hundreds of nano-seconds to a few micro-seconds, after an enable signal is applied to output a valid digital code. This time is needed for the purpose of the circuit startup and the AD conversion that may take place simultaneously.
During this time, other operations inside the semiconductor device comprising the analog sensor and the ADC, such as a charge pump rum on, are not recommended, because of possible power supply- or ground-induced disturbances, which would negatively affect the conversion operation of the ADC and the temperature sensing performed by the analog sensor. A possible disturbance during the startup and the conversion may eventually impact the semiconductor's operational characteristics such as a read time, a write time, a program time, and an erase time of the semiconductor device.
Accordingly, a novel ADC configuration is needed to reduce the impact of a power supply or ground disturbance in order to improve the performance of a semiconductor device.